1. Field of the Invention
The present invention relates to a photoelectron emitting member having a photoelectric effect, as well as a method of electrically charging fine particles using that member.
Fine particles electrically charged with photoelectrons have various applications such as
(a) separating and classifying fine particles, as well as modifying the surfaces thereof and controlling charge amounts; PA1 (b) measuring the concentration and size of fine particles in gases such as air and waste gases or in a space by using electrically charged fine particles; and PA1 (c) trapping and removing charged fine particles to produce clean gases or clean spaces. PA1 (1) Japanese Patent Public Disclosure (Laid-Open) No. 178050/1986 (corresponding to U.S. Pat. No. 4,750,917); PA1 (2) Japanese Patent Public Disclosure (Laid-Open) No. 24459/1987; PA1 (3) Japanese Patent Public Disclosure (Laid-open) No. 77557/1988; PA1 (4) Japanese Patent Public Disclosure (Laid-Open) No. 100955/1988; and PA1 (5) Japanese Patent Public Disclosure (Laid-Open) No. 262954/1989. PA1 (1) Japanese Patent Public Disclosure (Laid-Open) No. 242838/1987; PA1 (2) Japanese Patent Public Disclosure (Laid-Open) No. 47536/1990; and PA1 (3) Japanese Patent Application No. 134781/1989.
1. Prior Art
The present inventor has previously proposed many methods of electrically charging fine particles with photoelectrons that are emitted upon applying uv rays and/or other forms of radiation to a photoelectron emitting member and various applications of the thus formed photoelectron emitting member. In the method of producing clean gases proposed by the present inventor, the following are particularly relevant to the present invention:
With regard to the measurements, the following were proposed by the inventor:
With regard to the separation and classification, the following was proposed by the inventor: Japanese Patent Application No. 177198/1989 (not yet Laid-Open).
Further, with regard to the conditions of electrically charging fine particles, the following were proposed by the inventor: (1) Japanese Patent Application No. 120563/1989 (not yet Laid-Open) and (2) Japanese Patent Application No. 120564/1989 (not yet Laid-Open).
Furthermore, with regard to photoelectron emitting members, the following were proposed by the inventor: (1) Japanese Patent Application No. 155857/1989 (not yet Laid-Open) and (2) Japanese Patent Application No. 153335/1990 (not yet Laid-Open).
Conventional photoelectron emitting members are made of either single materials in bulk (mass) form or bulk materials having a protective film or a thin-film material provided on their surface. These members emit photoelectrons in a direction opposite to the direction of incidence of ultraviolet rays with which they are irradiated (in other words, photoelectrons are emitted as if they were reflected from the surface of those members). However, the use of these prior art photoelectron emitting members is limited and accordingly, there has been a room for improvement depending on the field of applications and the type of apparatus in which they are used. The problems are briefly described below with reference to an example.
FIG. 3 is a cross section of a conventional air cleaner, which comprises an ultraviolet lamp 1, an ultraviolet radiation transmitting window 2, a photoelectron emitting member 3, electrodes 4 for establishing an electric field, and a charged fine particle trapping plate 5. When air 6 containing fine particles is admitted into the air cleaner, the fine particles in the air are electrically charged with photoelectrons 7 emitted from the member 3 upon irradiation with ultraviolet rays and are trapped by the member 5, whereby clean air is produced at an outlet 8. In the air cleaner shown in FIG. 3, the photoelectron emitting member is provided on the other side of the apparatus which is remote from the uv lamp, so the dose of uv radiation applied to the surface of the photoelectron emitting member is significantly reduced, which is not desirable from the viewpoint of efficient energy use. Further, the apparatus of FIG. 3 does not have a high degree of design flexibility.